Leaf optical properties in amphibious plant species are affected by multiple leaf traits

The amphibious plant species Sagittaria sagittifolia and Ranunculus lingua here serve as model systems to study differences in leaf optical properties of different leaf types that develop in aquatic and terrestrial environments. We aimed to determine leaf traits that explain most of the variability in the reflectance and transmittance spectra in the range from 280 to 880 nm. Comparisons of leaves of the same form revealed marked differences in their structures and particularly in the content of total methanol-soluble UV-absorbing compounds. Submerged leaves transmit radiation over the whole range measured, but emerged leaves transmit only at wavelengths from 500 to 650 nm, and above 690 nm. Redundancy analysis shows that biochemical leaf traits, namely the UV-absorbing compounds chlorophyll a and b, together with the specific leaf area (SLA), significantly affect the reflectance spectra, explaining 60% of the spectra variability. Pigment levels negatively affect reflectance, while the effect of SLA is positive. Physical traits like thickness of the palisade mesophyll, SLA, and thickness of the lower and upper epidermis, along with anthocyanin content, explain 62% of the transmittance spectra variability. This study provides new insight into the understanding of data collected for aquatic and semi-aquatic plants based on spectral analyses.